Heat exchanger with tube bundle

ABSTRACT

A heat exchanger includes a tube bundle including a plurality of heat exchanger tubes, each of the heat exchanger tubes having an inlet, an outlet, an outer surface, and a generally U-shaped bend region disposed between at least two straight tube ends, wherein at least a portion of the at least two straight tube ends includes flat tubes, a jacket part disposed around the tube bundle to enclose at least a portion of the tube bundle, wherein an interior is formed between the tube bundle and the jacket part to receive a coolant around the outer surface of each of the heat exchanger tubes, and a casing cover coupled to the jacket part to form a fluid tight seal therebetween, wherein the inlet and the outlet of each of the heat exchanger tubes fluid-tightly passes through the casing cover and extends outside of the casing cover.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application Serial Number DE 10 2009 047 620.2 filed Dec. 8, 2009, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a heat exchanger, particularly an exhaust gas heat exchanger with a tube bundle.

BACKGROUND OF THE INVENTION

Heat exchangers of the above mentioned kind serve to cool exhaust gas, particularly of internal combustion engines. Specifically, a cooled exhaust gas is added to a fresh air that is fed to the combustion process so that the oxygen content is minimized. Additionally, heat exchangers are configured to utilize a thermal energy inherent to the exhaust gas. A heat exchanger is typically used at a suction side of supercharged engines, at fuel cells, or in other cases. For use in a vehicle with an internal combustion engine, the most important field of application of the heat exchanger with a tube bundle, it is also required to minimize the structural volume.

WO 00/00778 describes a flat tube heat exchanger, where differently oriented flat tubes are formed U-shaped, in the U-region established as circular cross-section tubes. Fins are required between the U-shaped flat tubes to ensure optimum heat transfer to the surrounding medium. However, the heat exchanger of WO 00/00778 is disadvantageous in that fins are necessary so that the heat exchanger requires more technical effort and space.

DE 10 2008 001 660 A1 describes a lightweight flow heat exchanger, wherein an exhaust gas conducting exchanger tube arranged separate is placed in a closed casing arranged separate. The casing is passed by a coolant that flows around the outside of the exchanger tube. Both ends of the exchanger tube are fluid-tightly passed through the casing cover that tightly closes the jacket part. Therefore, the inlet and outlet of the exchanger tube are located outside the casing. The exchanger tube is designed as circular-section tube with different forms that enlarge the surface and break up the flow. However, a disadvantage of the heat exchanger of DE 10 2008 001 660 A1 is the small heat exchanger area and thus, lower heat exchanging capacity related to the structural space of the heat exchanger. Circular cross-section tubes, further, have limited heat emitting properties.

DE 197 56961 A1 describes an arrangement of a heat exchanger with tubes that are arranged establishing one row next to each other and at least two rows behind each other and parallel to each other. The tubes are heat transmittingly connected to cooling members designed as cooling fins. Two tubes each form the legs of a tube fork made as one part, communicatingly connected to each other through a curved piece. The tubes are established as flat tubes, having two planar longer side surfaces arranged parallel to each other and two shorter side surfaces connecting the longer side surfaces to each other. The cooling fins each extend at least between adjacent flat tubes, the fins being heat transmittingly attached to the longer side surfaces of the fins. The heat exchanger of DE 197 56961 A1 is disadvantageous due to the expensive use of cooling fins, which furthermore are not suitable with a liquid coolant that flows around the external surfaces of the tubes.

Other disadvantages and deficiencies of the prior art are the high space requirements of a heat exchanger, which can be problematic, especially in a motor vehicle where only limited space can be made available for the components. To solve this problem, the prior art offers the use of fins that can help to enlarge the heat exchanger surface. But volume reduction in proportion to the additional expense that results from the manufacture of heat exchanger tubes covered with fins is comparatively little.

Tube bundles of tubes with circular cross-section achieve less package density, or larger clearances develop between the circular cross-sections, respectively, compared to other cross-sectional geometries such as triangular, rectangular or flat tube cross-sections. In addition, the clearances between the circular cross-sections are less accessible to the medium that flows around them, because the cross-sectional area of the inlet into the clearance cross-sectional area is correspondingly narrow compared to the clearance cross-sectional area. For the other cross-sections mentioned above, the ratio between the inlet and clearance cross-sectional areas is balanced.

In the prior art a U-passage is frequently obtained using straight tubes and a reversing geometry (scoop). Therefore, in the region of reversal, no heat is transferred, but additional pressure losses develop resulting from one additional outflow and inflow process each in the reversal region.

Certain disadvantages of the prior art can be overcome by the use of circular cross-section tubes bent in generally U-shape formations. However, the disadvantage of low heat exchanger capacity due to the maximized ratio of the cross-sectional area to the perimeter of the circular cross-section and the minimum heat exchanger area resulting therefrom continues to exist.

SUMMARY OF THE INVENTION

The invention overcomes the shortcomings of the prior art by providing a heat exchanger with a tube bundle, wherein a structural volume of the heat exchanger is minimized without any loss in heat exchanger capacity, while dispensing with fins and minimizing a pressure loss.

The present invention provides the heat exchanger with a heat exchanger tube that is established separate. The heat exchanger tube is placed in a closed casing that is established separate, passed by a coolant. The coolant flows around the heat exchanger tube at the outside.

The casing establishes at least a casing cover and a jacket part, whereby the jacket part is tightly closed by the casing cover, both ends of the exchanger tube being fluid-tightly passed through the casing cover. Thereby, the inlet and outlet of the exchanger tube are located outside the casing.

Further, part of the solution is a tube bundle provided with a U-shaped bend region and straight tube ends. At least in the region of the straight tube ends, the tube bundle is made of flat tubes. Flat tubes have two plane longer side surfaces arranged parallel to each other and two shorter side surfaces connecting the longer side surfaces to each other. A cross-sectional flow area is generally rectangular, having two long sides and two short sides each opposing one to the other. Other flat tubes have cross-sections with two long sides connected through semicircular elements.

The advantage of this solution, particularly, is that with the flat tube, a tube cross-section is employed that enables a high heat exchanger capacity to be obtained as a large surface area compares to a small cross-sectional area.

Further, the problem of the invention is solved by that the U-shaped bend region has a cross-sectional shape different from the flat tube cross-section of the straight tube ends.

In addition, according to the invention, the straight tube ends of the flat tubes oppose each other with their narrow sides in the heat exchanger. In an alternative embodiment of the invention, the straight tube ends of the flat tubes oppose each other with their wide sides. That means, in case the entire tube inclusive of the U-shaped bend region is made of flat tube, that in one alternative embodiment the tube is bent in the narrow side plane and in another alternative embodiment the tube is bent in the wide side plane.

The advantage of bending in the narrow side plane is technological, as the section modulus is lower in this direction so that the U-shape can be obtained easier.

If bending is executed in the wide side plane, the section modulus is high. Apart from bending in the wide side plane of the cross-section of the flat tube, the flat geometry in the reversing region can also be produced in an alternative manner. But this solution is advantageous in that the wide side of the flat tube extends in direction of flow of the coolant that circulates in the casing of the heat exchanger. Therefore, optimal heat transfer is achieved.

In an advantageous further embodiment of the invention, the tube cross-section in the U-shaped bend region has a circular cross-sectional shape. In advantageous embodiments of the invention, the cross-section of the tube in the U-shaped bend region alternatively has rectangular or oval-shaped cross-sectional shapes.

The use of a circular cross-section is technologically advantageous as bending the flat tube is no longer necessary, the bending could be especially problematic if to be executed in the wide side plane of the profile. Further, a circular cross-section in the U-shaped bend region enables optimal flow conditions to be realized. This is particularly important if when the bend is established using a flat tube, it cannot be ensured that bending will not lead to a narrowed cross-section.

In a particularly advantageous embodiment, the tubes of the tube bundle are provided with a structured surface. The structure in one embodiment consists of square recesses in the tube outside that are distanced from each other such that the distances are approximately double the side length of the squares. In alternative embodiments of this aspect of the invention, the structure consists of annular or helical grooves formed in the tube walls.

The establishment of a structure in the tube walls leads to an advantageous turbulence of the flow, above all, inside the tube, to a breaking up of the laminar flow and the boundary layer. This leads to an improved heat transfer between the medium flowing in the tube and the tube wall so that the capacity of the heat exchanger rises.

It is also useful to combine several U-shaped tubes with each other in the tube bundle. Here, it is advantageous if always at least two U-shaped tubes with equal radii of the U-shaped bend and equal lengths of the straight flat tube ends are located side by side and always at least two U-shaped tubes with different radii each are located below each other.

By combining the U-shaped tubes with each other, a large area active in heat transfer develops within a small volume. Thus the heat exchanger reaches high capacity, while demanding only little structural space.

It has been shown to be particularly useful to arrange the bend regions of the heat exchanger tubes of the tube bundle alternatingly offset to each other. By skillfully arranging the alternating offset, a high package density can be achieved, although in the reversal region, a transition to a circular geometry is provided.

According to an embodiment of the invention, the heat exchanger is designed such that it is used in the exhaust gas string of a motor vehicle. For that, the casing cover forms an interface for the connection of the heat exchanger to the exhaust system of the motor vehicle.

The advantages of the heat exchanger according to the invention have a particular effect in a motor vehicle, where the available installation space is restricted. A heat exchanger optimized in that way, providing a high capacity of heat transfer while requiring little space is, therefore, very well suited for the use in a motor vehicle.

It is useful when the heat exchanger is provided with a plurality of heat exchanger tubes located in the casing, which establish a tube bundle fluidly switched in parallel.

Due to the parallel connection of the heat exchanger tubes, higher rates of exhaust gas can be passed through the heat exchanger, extracting heat from the exhaust gas.

In an advantageous embodiment of the invention, a coolant inlet and a coolant outlet are arranged, the coolant inlet and/or the coolant outlet positioned in the casing cover.

Due to the integration of the coolant inlet and the coolant outlet into the casing cover, all interfaces are integrated into one structural member and at one place. Therefore, particularly for the use in a motor vehicle, the final assembly of the vehicle when also the heat exchanger is to be installed is improved and made easier. Thus, all interfaces can be integrated into a narrow space and connected to the heat exchanger in one mounting step.

It has shown that the heat exchanger is designed such that it can advantageously be used in the coolant-cooled charge air cooler of a motor vehicle. Here, the coolant cools the hot compressed fresh air coming from the turbocharger.

Another advantageous field of use of the heat exchanger is a coolant-cooled oil cooler of a motor vehicle. The heat exchanger is particularly suitable for cooling hot engine oil using a coolant.

A particularly positive aspect of the invention is the possibility that the jacket part of the casing is made of a material with a melting temperature of below 1000° C. Surprisingly, it has shown that for the jacket part, materials can be used that must only meet the requirements resulting from the use of the cooling medium. This relates, first, to pressure, temperature and chemical resistance. Chemical resistance is particularly important when oil is used as the cooling medium. Thus, even if the heat exchanger is used as an exhaust gas cooler, materials with a low melting temperature far less than 1000° C., such as plastics or aluminum, can be used for the jacket part. These materials would normally not withstand the exhaust gas temperatures. This advantage results from the use of U-tubes for heat transfer as well as from that the shape is a closed U-bent shape. Additionally, the favorable possibility arises to be very free to choose the material of the cooler casing so that also light, inexpensive materials can be employed, which is decisive for the weight and the price of the final product.

Altogether, the advantages of the invention are an increased heat exchanger capacity in a small structural space, an increased degree of freedom in arranging the U-bent heat exchanger tubes so that a higher package density is made possible. The heat exchangers according to the invention are smaller and lighter. Due to the higher heat transfer efficiency of the heat exchanger, material is saved compared with heat exchangers of the prior art with the same capacity.

In one embodiment, a heat exchanger comprises: a tube bundle including a plurality of heat exchanger tubes, each of the heat exchanger tubes having an inlet, an outlet, an outer surface, and a generally U-shaped bend region disposed between at least two straight tube ends, wherein at least a portion of the at least two straight tube ends includes flat tubes; a jacket part disposed around the tube bundle to enclose at least a portion of the tube bundle, wherein an interior is formed between the tube bundle and the jacket part to receive a coolant around the outer surface of each of the heat exchanger tubes; and a casing cover coupled to the jacket part to form a fluid tight seal therebetween, wherein the inlet and the outlet of each of the heat exchanger tubes fluid-tightly passes through the casing cover and extends outside of the casing cover.

In another embodiment, a heat exchanger comprises: a tube bundle including a plurality of heat exchanger tubes, each of the heat exchanger tubes having an inlet, an outlet, a structured outer surface, and a generally U-shaped bend region disposed between at least two straight tube ends, wherein at least a portion of the at least two straight tube ends includes flat tubes, and wherein a bend region of at least one of the heat exchanger tubes has at least one of a generally circular cross-sectional shape, a generally oval cross-sectional shape, and a generally rectangular cross-sectional shape; a jacket part disposed around the tube bundle to enclose at least a portion of the tube bundle, wherein an interior is formed between the tube bundle and the jacket part to receive a coolant around the outer surface of each of the heat exchanger tubes; and a casing cover coupled to the jacket part to form a fluid tight seal therebetween, wherein the inlet and the outlet of each of the heat exchanger tubes fluid-tightly passes through the casing cover and extends outside of the casing cover.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, features and advantages of the invention will become apparent from the following description of exemplary embodiments in combination with the accompanying drawings. It is shown by:

FIG. 1 a: heat exchanger with tube bundle of flat tube in top view;

FIG. 1 b: heat exchanger with tube bundle of flat tube in front view;

FIG. 1 c: heat exchanger with tube bundle of flat tube in side view;

FIG. 2: heat exchanger with tube bundle of flat tube in exploded view;

FIG. 3 a: heat exchanger with tube bundle of transversally bent flat tube in top view;

FIG. 3 b: heat exchanger with tube bundle of transversally bent flat tube in front view;

FIG. 3 c: heat exchanger with tube bundle of transversally bent flat tube in side view;

FIG. 4: heat exchanger with tube bundle of transversally bent flat tube in exploded view;

FIG. 5 a: heat exchanger with tube bundle of flat tube and circular-section tube in top view;

FIG. 5 b: heat exchanger with tube bundle of flat tube and circular-section tube in front view;

FIG. 5 c: heat exchanger with tube bundle of flat tube and circular-section tube in side view;

FIG. 6 a: casing and seal of the heat exchanger with tube bundle of flat tube and circular-section tube in perspective representation;

FIG. 6 b: tube bundle and casing cover of the heat exchanger of flat tube and circular-section tube in perspective representation;

FIG. 6 c: tube bundle and casing cover of the heat exchanger with flat tube and circular-section tube in side view;

FIG. 7 a: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube in top view;

FIG. 7 b: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube in front view;

FIG. 7 c: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube in side view;

FIG. 8 a: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube—tube bundle and casing cover—in perspective representation;

FIG. 8 b: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube—jacket part with seal—in perspective representation;

FIG. 8 c: heat exchanger with tube bundle of transversally arranged flat tube and circular-section tube—tube bundle and casing cover—in side view;

FIG. 9 a: heat exchanger with offset arranged tube bundle of flat tube and circular-section tube—in top view;

FIG. 9 b: heat exchanger with offset arranged tube bundle of flat tube and circular-section tube—in front view;

FIG. 9 c: heat exchanger with offset arranged tube bundle of flat tube and circular-section tube—in side view;

FIG. 10 a: heat exchanger with offset arranged tube bundle of transversally arranged flat tube and circular-section tube in top view;

FIG. 10 b: heat exchanger with offset arranged tube bundle of transversally arranged flat tube and circular-section tube in front view;

FIG. 10 c: heat exchanger with offset arranged tube bundle of transversally arranged flat tube and circular-section tube in side view;

FIG. 11 a: heat exchanger with offset arranged tube bundle of transversally arranged flat tube and circular-section tube in perspective representation;

FIG. 11 b: casing of a heat exchanger in perspective representation;

FIG. 12 a: heat exchanger with offset arranged tube bundle of flat tube and circular-section tube in perspective representation;

FIG. 12 b: casing of a heat exchanger in perspective representation;

FIG. 13 a: heat exchanger with offset arranged tube bundle of transversally arranged flat tube and circular-section tube in perspective representation; and

FIG. 13 b: casing of a heat exchanger in perspective representation.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The following detailed description and appended drawings describe and illustrate various embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.

FIG. 1 a shows a heat exchanger 1 with tube bundle 15 of flat tube in top view, wherein the narrow sides of the flat tubes that form the heat exchanger tube 6 are seen. Both the straight tube ends 2 and the bend region 3 consist of flat tube that in the bend region 3 was bent in the narrow side plane. Arrows identify the direction of flow of the inflowing gas with the inlet 12 and the outlet 13 marked separately. Inlet 12 and outlet 13 are passed through the casing cover 4.

Several heat exchanger tubes 6, established matching into each other due to bend regions 3 of different radii, together form the tube bundle 15.

FIG. 1 b shows a heat exchanger 1 with tube bundle 15 of flat tube in front view, showing the arrangement of the ends 11 of the heat exchanger tubes 6 on the casing cover 4. Thus, the tube bundle 15 is established such that always three heat exchanger tubes 6 with different radii in the bend region 3 that match into each other are arranged in each other, and always three of these groups are arranged side by side so that always nine inlets 12 and outlets 13 pass the casing cover 4.

FIG. 1 c shows a heat exchanger 1 with tube bundle 15 of flat tube in side view with the wide side of the heat exchanger tubes 6 established as flat tube seen. The straight tube ends 2 turn into the bend region 3 at one end, at the other end forming the ends 11 of the heat exchanger tube 6.

FIG. 2 shows a heat exchanger 1 with tube bundle 15 of flat tube in exploded view, whereby in the upper region of the figure, the jacket part 5 with the seal 14 is seen, which when the casing 5 is closed ensures tight closure of the coolant filled interior against the environment. In the lower region, the tube bundle 15 is shown connected to the casing cover 4. The heat exchanger tubes 6, bent U-shaped in the narrow side plane, established as flat tubes, can be seen forming the tube bundle 15 in dense package within each other and arranged side by side based on different radii in the bend region 3.

The ends 11 of the heat exchanger tube 6 pass the casing cover 4 and are fixed in the casing cover 4. After having passed the casing cover 4, the heat exchanger tubes 6, or their ends 11, respectively, form the interface 7 that serves to connect the heat exchanger 1 to the exhaust gas system of a motor vehicle. In detail, the exhaust gas then enters the inlet 12, and after the heat has been transferred, the cooled exhaust gas exits the heat exchanger 1 through the outlet 13.

The heat energy carried by the exhaust gas, which exits the combustion chamber of the engine at high temperature, is dissipated to a coolant. The coolant flows into the heat exchanger 1, especially the jacket part 5 of the casing. Hereby, the coolant enters and exits through the openings in the casing cover 4, the coolant inlet 9 and the coolant outlet 10. In order to avoid short circuit flows within the casing, a partition wall 8 is attached to the casing cover 4, the partition wall 8 projecting into the U-shaped bend of the heat exchanger tube 6 with the smallest radius. This forces the coolant to flow largely along the heat exchanger tubes 6 instead of on the shortest way near to the casing cover 4 from the coolant inlet 9 to the coolant outlet 10.

In one embodiment, the jacket part 5 of the casing is made of a material with a low melting temperature, especially a plastic material. But it can be also made of other materials with low melting temperatures, such as aluminum. The material used must only meet the requirements set by the use of the cooling medium. The requirements relate, first of all, to pressure, temperature and chemical resistance. Chemical resistance is particularly important when oil is used as the cooling medium. Also, cooling water with additives can make specific demands to the chemical resistance. Thus, even in the exemplary case of use of the heat exchanger as exhaust gas cooler, materials with a low melting temperature, which can be far below 1000° C., such as plastics or aluminum, can be used for the jacket part 5. These materials would normally not withstand the exhaust gas temperatures. Thus, the favorable possibility arises to be very free to choose the material of the cooler casing, especially the jacket part 5, so that also light, inexpensive materials can be employed, which is decisive for the weight and the price of the finished product.

FIG. 3 a shows a heat exchanger 1 with tube bundle 15 of transversally bent flat tube in top view, wherein as distinct from FIG. 1 a view is in direction of the wide side of the flat tube. Also, here, the whole heat exchanger tube 6 completely consists of a flat tube. In the embodiment shown, the flat tube was given a U-shape in the wide side plane.

FIG. 3 b shows a heat exchanger 1 with tube bundle 15 of transversally bent flat tube in front view, wherein, as in the representation of FIG. 1 b, the casing cover 4 is shown with the tube passages arranged homogeneous. Due to the orientation of the cross-section of the flat tubes, only two U-shaped bends of the heat exchanger tube 6 are arranged within each other, but five of these couples are staggered above each other. Therefore, there are 10 inlets 12 and 10 outlets 13 each, through which the exhaust gas enters and exits, respectively, the heat exchanger 1.

Bending the flat tube in the wide side plane is technologically difficult, demanding a special technological solution.

FIG. 3 c shows a heat exchanger 1 with tube bundle 15 of transversally bent flat tube in side view with the view in direction of the narrow side of the heat exchanger tubes 6 which are established as flat tubes. The straight tube end 2 turns into the bend region 3.

FIG. 4 shows a heat exchanger 1 with tube bundle 15 of transversally bent flat tube, which is used as heat exchanger tube 6, in exploded representation. The upper part of the figure shows the jacket part 5 of the casing and the accompanying seal 14.

The lower part of the figure shows the tube bundle 15, which consists of heat exchanger tubes 6, connected to the casing cover 4. The heat exchanger tubes 6 are arranged such that the U-shaped bend is in the wide side plane. The complete heat exchanger tubes 6, both the straight tube end 2 and the bend region 3 as well, are made of flat tube.

While the tube bundle 15 projects from the top of the casing cover 4, the interface 7 is positioned at the bottom.

FIG. 5 a shows a heat exchanger 1 with tube bundle 15 of flat tube and circular-section tube in top view, wherein, as distinct from the above representations, particularly FIG. 1 a with the same view to the narrow sides of the flat tubes, the heat exchanger tubes 6 are not exclusively made of flat tube. The straight tube ends 2, which are made of flat tube, in the bend region 3 turn to circular-section tubes. The whole bend region 3 is made of tubes with circular cross-section.

The changing cross-section changes the flow conditions in the bend region 3, or in the transition region between the straight tube end 2 and the bend region 3, respectively. Turbulence develops at the point of inflow into the bend region 3 with circular cross-section. Also, the flow resistance, which in the bend region 3 is higher than in a straight tube, reduces due to the enlarged cross-section.

FIG. 5 b shows a heat exchanger 1 with tube bundle 15 not shown, of flat tube and circular-section tube in front view, whereby the arrangement of the tube passages through the casing cover 4 is not different from the representation in FIG. 1 b.

FIG. 5 c shows the tube bundle 15 of a heat exchanger 1 of fiat tube and circular-section tube in side view with the wide sides of the straight tube ends 2 seen. Also seen is a transition region 16, which shows trapezoidal in the side view. This transition region serves to match the rectangular cross-section of the flat tube with the circular cross-section of the tube section that forms the bend region 3.

FIG. 6 a shows casing 5 and seal 14 of the heat exchanger 1 with tube bundle 15 of flat tube and circular-section tube in perspective representation. The jacket part 5 and the seal 14 are seen.

FIG. 6 b shows tube bundle 15 and casing cover 4 of the heat exchanger 1 of flat tube and circular-section tube in perspective representation. The casing cover 4 accommodates the straight tube ends 2, which at the bottom of the casing cover 4 form the interface 7. Apart from the straight tube ends 2, the heat exchanger tubes 6 are formed of the bend regions 3. The bend region 3, as distinct to the straight tube end 2 that is made of flat tube, is made of tube with circular cross-section.

FIG. 6 c shows tube bundle 15 and casing cover 4 of the heat exchanger 1 with flat tube and circular-section tube in side view with at least the wide sides of the outer heat exchanger tubes 6 that are formed of flat tube to be seen. Flat tubes, however, are only used in the region of the straight tube ends 2, while the bend region 3 is formed of tubes with circular cross-section. This feature of one embodiment of the invention shows in the side view as reduced width of the heat exchanger tube 6 in the bend region 3.

FIG. 7 a shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube in front view. The flat tubes of a communicating tube bend of the heat exchanger 1 are oriented with the shorter sides to each other. Communication of the two straight tube ends 2 at their upper ends is over the bend region 3, which in the example of embodiment represented is made of circular-section tube. A transition region 16 ensures the match of the cross-sections of flat tube and circular-section tube. The fluid-tight passage 17 seals the interior of the heat exchanger 1 from the environment in the region of the tube passages.

FIG. 7 b shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube in top view, wherein the arrangement of the passages of the straight tube ends 2 through the casing cover 4 shows that five inner and five outer bend-shaped heat exchanger tubes 6, not shown in the figure, are located on the casing cover 4.

FIG. 7 c shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube in side view, showing the flat side of the flat tubes that form the straight tube ends 2. Over the transition region 16, the flat tube turns into the circular-section tube, forming the bend region 3 in the example of embodiment shown. In this further embodiment of the solution according to the invention, it is particularly advantageous that the heat exchanger tubes 6 positioned one above the other are in a skillful alternatingly offset arrangement. This allows, in spite of changing to a circular geometry, to achieve a high packaging density in the bend region 3, the region of reversal.

FIG. 8 a shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube in perspective representation, wherein tube bundle 15 and casing cover 4 are seen in detail. Coolant inlet 9 and coolant outlet 10 are arranged in the casing cover 4. In order to avoid short circuit flows between the coolant inlet 9 and the coolant outlet 10 the partition 8 is positioned in the possible short circuit flow path, extending between the casing cover 4 and the bend region 3.

FIG. 8 b shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube in perspective representation, whereby here the jacket part 5 with the seal 14 is shown.

FIG. 8 c shows a heat exchanger 1 with tube bundle 15 of transversally arranged flat tube and circular-section tube, again with the representation of tube bundle 15, partition 8 and casing cover 4, but in side view. It is seen how the flat tube, seen as narrow in this view, of the straight tube end 2 turns into the wider circular-section tube of the bend region 3, located on the right-hand side of the figure.

With this alternative of the solution according to the invention, it has shown to be particularly useful that the heat exchanger tubes 6 positioned one above the other are in a skilful alternatingly offset arrangement. This allows, in spite of changing to a circular geometry, to achieve a high packaging density in the bend region, or the region of reversal, respectively.

FIG. 9 a shows a heat exchanger 1 with offset arranged tube bundle 15 of flat tube and circular-section tube in top view. Here the straight tube ends 2 that over the transition region 16 turn into the bend region 3 are shown. In the shown example of embodiment, the bend region 3 is made of circular-section tube, seen in the figure by the cross-section enlarged in the bend region 3. The heat exchanger tubes 6, established as flat tubes, in one embodiment of the invention shown are arranged such that the wide sides of the flat tubes oppose each other. Three groups of bend-shaped heat exchanger tubes 6 each of a different height are positioned below each other or within each other.

Arrows indicate the direction of flow of the fluid in the tubes, which in certain embodiments is the exhaust gas of an internal combustion engine.

FIG. 9 b shows the casing cover 4 of a heat exchanger 1 in front view. The passages of the straight tube ends 2, which are established passing the casing cover 4 fluid-tightly sealed, are arranged offset. Three groups of bend-shaped heat exchanger tubes 6, not shown in the figure, each of a different height, are positioned slightly offset transverse to the direction of flow, with in one embodiment, the offset being half the length of the long side of the cross-section of the flat tube.

The groups of bend-shaped heat exchanger tubes 6, which together form the tube bundle 15 also not shown in this figure, consist of flat tube and circular-section tube, with the flat tube used in the region of the straight tube end 2, the circular-section tube used in the bend region 3.

FIG. 9 c shows offset arranged tube bundles 15 of a heat exchanger 1 in side view, with the tube bundles 15 consisting of flat tube and circular-section tube. Here the wide side of the flat tubes is seen that establish the region of the straight tube end 2. Behind a transition region 16, the heat exchanger tube 6 turns to the bend region 3 established as circular-section tube.

FIG. 10 a shows a heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in top view. In the embodiment shown, the heat exchanger tubes 6, established as flat tubes, are arranged such that the narrow sides of the flat tubes oppose each other. Three groups of bend-shaped heat exchanger tubes 6, each of a different height, are positioned below each other and within each other, respectively.

It is particularly useful that the heat exchanger tubes 6 positioned one above the other are in a skilful alternatingly offset arrangement. This allows, in spite of turning into a circular geometry, to achieve a high packaging density in the bend region, or the region of reversal, respectively.

FIG. 10 b shows a heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in front view. The passages of the straight tube ends 2 are seen on the casing cover 4. Of the three groups of the straight tube ends 2, each comprising an inlet 12 and an outlet 13 and each being part of heat exchanger tubes 6 with different bend height, not shown here, the passages each of the inlet 12 and outlet 13 are marked on the casing cover 4. In the embodiment shown, each group includes five single heat exchanger tubes 6.

FIG. 10 c shows the tube bundle 15 of a heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in side view. This view enables to see the narrow sides of the flat tubes that establish the straight tube ends 2. On the right-hand side of the figure, the transition region 16 and further, the cross-section of the circular-section tube that establishes the bend region 3 are shown.

FIG. 11 a shows a heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in perspective representation, the tube bundle 15 comprising a plurality of heat exchanger tubes 6, eleven tubes in the embodiment shown here, in dense package. The flat tubes oppose each other with their narrow sides. The heat exchanger tubes 6 are anchored in the casing cover 4, which on its rear establishes the interface 7.

FIG. 11 b shows the heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in exploded representation with the jacket part 5 and the seal 14 shown, but the tube bundle 15 of transversally arranged flat tube and circular-section tube is not shown.

FIG. 12 a shows a heat exchanger 1 with offset arranged tube bundle 15 of flat tube and circular-section tube in perspective representation, the tube bundle 15 comprising a plurality of heat exchanger tubes 6, eleven tubes in the embodiment shown here, in dense package. The flat tubes oppose each other with their wide sides.

The heat exchanger tubes 6 are anchored in the casing cover 4, which on its rear establishes the interface 7. The partition 8, which vertically projects from the casing cover 4, prevents short circuit flows of the coolant that circulates freely within the heat exchanger 1.

FIG. 12 b shows the heat exchanger 1 with offset arranged tube bundle 15 of flat tube and circular-section tube in exploded representation with the jacket part 5 and the seal 14 shown, but the tube bundle 15 of flat tube and circular-section tube is not shown.

The outer surface of the heat exchanger tubes 6 used in the previous examples is provided with a helically embossed groove. Alternatively to this embodiment, also a smooth heat exchanger tube 6 without embossing can be used.

FIG. 13 a shows the heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in perspective representation. Distinct to the embodiment shown in FIG. 12 a with smooth or helically grooved tube wall of the heat exchanger tube 6, the tube wall of the alternative embodiment shown here is more intensely structured. The structure is applied to both the region of the straight tube ends 2 and the bend region 3. In the embodiment shown, a structure of square recesses is used. The square recesses are applied to the wide side of the flat tube, are arranged mosaic-like offset and project into the flow cross-section of the flat tube. Thus, they prevent a laminar flow from being developed and whirl the exhaust gas in the heat exchanger tubes 6, the exhaust gas flowing in the heat exchanger tubes 6 in certain embodiments of the invention. Due to the whirls, also a developing boundary layer is broken up so that heat transfer improves. The structure also enlarges the heat exchanger surface, which additionally enhances the heat exchanger capacity. Apart from the mosaic-like structure, also annular or helical structures and a smooth surface of the wall of the heat exchanger tube 6 is provided according to the invention.

FIG. 13 b shows the heat exchanger 1 with offset arranged tube bundle 15 of transversally arranged flat tube and circular-section tube in exploded representation with the jacket part 5 and the seal 14 shown, but the tube bundle 15 of flat tube and circular-section tube not shown.

From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.

NOMENCLATURE

-   1 heat exchanger -   2 straight tube end -   3 bend region -   4 casing cover -   5 jacket part, casing -   6 heat exchanger tube -   7 interface -   8 partition -   9 coolant inlet -   10 coolant outlet -   11 ends of the heat exchanger tube -   12 inlet heat exchanger tube -   13 outlet heat exchanger tube -   14 seal -   15 tube bundle -   16 transition region -   17 passage 

1. A heat exchanger comprising: a tube bundle including a plurality of heat exchanger tubes, each of the heat exchanger tubes having an inlet, an outlet, an outer surface, and a generally U-shaped bend region disposed between at least two straight tube ends, wherein at least a portion of the at least two straight tube ends includes flat tubes; a jacket part disposed around the tube bundle to enclose at least a portion of the tube bundle, wherein an interior is formed between the tube bundle and the jacket part to receive a coolant around the outer surface of each of the heat exchanger tubes; and a casing cover coupled to the jacket part to form a fluid tight seal therebetween, wherein the inlet and the outlet of each of the heat exchanger tubes fluid-tightly passes through the casing cover and extends outside of the casing cover.
 2. The heat exchanger according to claim 1, wherein the bend region of at least one of the heat exchanger tubes has a cross-sectional shape different from a cross-sectional shape of the straight tube ends.
 3. The heat exchanger according to claim 1, wherein the straight tube ends are arranged such that a narrow side of each of the flat tubes of adjacent ones of the straight tube ends oppose each other.
 4. The heat exchanger according to claim 1, wherein the straight tube ends are arranged such that a wide side of each of the flat tubes of adjacent ones of the straight tube ends oppose each other.
 5. The heat exchanger according to claim 1, wherein the bend region of at least one of the heat exchanger tubes has a circular cross-sectional shape.
 6. The heat exchanger according to claim 1, wherein the bend region of at least one of the heat exchanger tubes has a rectangular cross-sectional shape.
 7. The heat exchanger according to claim 1, wherein the bend region of at least one of the heat exchanger tubes has an oval cross-sectional shape.
 8. The heat exchanger according to claim 1, wherein at least one of the heat exchanger tubes is provided with a structured surface.
 9. The heat exchanger according to claim 1, wherein the heat exchanger tubes are coupled to each other.
 10. The heat exchanger according to claim 1, wherein the bend region of each of a first pair of adjacent ones of the heat exchanger tubes have a generally equal radius with each other and the straight tube ends of each of the first adjacent pair of the heat exchanger tubes have a generally equal length with each other, wherein the bend region of each of a second pair of adjacent ones of the heat exchanger tubes have a different radius from each other.
 11. The heat exchanger according to claim 1, wherein the bend regions of adjacent ones of the heat exchanger tubes are arranged in an alternating offset arrangement.
 12. The heat exchanger according to claim 1, wherein the casing cover establishes an interface for a connection of the heat exchanger to a exhaust gas system of a motor vehicle.
 13. The heat exchanger according to claim 1, wherein each of the heat exchanger tubes is fluidically switched in parallel.
 14. The heat exchanger according to claim 1, wherein the casing cover includes a coolant inlet and a coolant outlet.
 15. The heat exchanger according to claim 1, wherein the jacket part of the casing is formed from a material with a melting temperature of below 1000° C.
 16. The heat exchanger according to claim 1, further comprising a partition wall coupled to the casing cover and projecting into the bend region of the one of the heat exchanger tubes with the smallest radius.
 17. The heat exchanger according to claim 1, wherein at least one of the heat exchanger tubes includes a plurality of spaced part recesses in the outside surface thereof.
 18. The heat exchanger according to claim 17, wherein the recesses have a generally square shape.
 19. The heat exchanger according to claim 1, wherein at least one of the heat exchanger tubes includes a groove formed in the outside surface thereof.
 20. A heat exchanger comprising: a tube bundle including a plurality of heat exchanger tubes, each of the heat exchanger tubes having an inlet, an outlet, a structured outer surface, and a generally U-shaped bend region disposed between at least two straight tube ends, wherein at least a portion of the at least two straight tube ends includes flat tubes, and wherein a bend region of at least one of the heat exchanger tubes has at least one of a generally circular cross-sectional shape, a generally oval cross-sectional shape, and a generally rectangular cross-sectional shape; a jacket part disposed around the tube bundle to enclose at least a portion of the tube bundle, wherein an interior is formed between the tube bundle and the jacket part to receive a coolant around the outer surface of each of the heat exchanger tubes; and a casing cover coupled to the jacket part to form a fluid tight seal therebetween, wherein the inlet and the outlet of each of the heat exchanger tubes fluid-tightly passes through the casing cover and extends outside of the casing cover. 